In accordance with the principles of transplantation immunology, transplanted tumors usually grow just as well in semi-syngeneic F1 offspring of their syngeneic hosts as in the latter, whereas the same tumor is rapidly rejected by the allogeneic counterpart as a consequence of allorecognition of the tumor cell's MHC/peptide complexes [7], representing the two extremes of tumor tolerance vs tumor rejection. The gene discussed is HLA-C; the disease is neoplasm.